The present invention relates to a repairing system for the emergency-repairing of a reactor vessel and in-pile structures in, for example, a nuclear power plant or the like, and a repairing method.
Sructures of a light-water reactor, such as a boiling-water reactor, are formed of materials having a sufficient corrosion resistance and high-temperature strength in an environment of high temperatures, such as austenitic stainless steels or nickel-base alloys.
However, there is apprehension about the quality degradation of the materials of the members difficult to change of the structures due to exposure to a severe environment during the long-term operation of the plant or the detrimental irradiation with neutrons. Particularly, weld zones are subject to the potential danger of stress-corrosion cracking due to the sensitization of the materials by weld heat input and residual tensile stress.
A shroud supporting fuel assemblies, among the structures, is particularly subject to the influence of neutrons produced by the fuel assemblies and is highly subject to stress-corrosion cracking. Various working systems for the inspection for soundness and preventive maintenance of structures highly subject to damaging danger have been invented and practically applied. However, since those working systems are intended to carry out work efficiently for entire weld lines, the working systems are large, need much time for preparatory work, are large in scale and complicated and need well-trained operators for operation. Thus, the conventional working systems are unable to take such steps as occasion demands and to meet the demands of occasion.
The present invention has been made in view of those problems and it is therefore an object of the present invention to provide a partial-repairing system capable of dealing with various tasks somewhat efficiently, through, and of being inserted and installed in a reactor instantly, and highly maneuverable, and a repairing method.
A modular submersible repairing system according to the present invention includes a working unit; and a base unit; wherein the working unit includes: at least one type of tool module repairing structures in a reactor, a scanning/pitching module being selectively connected to or disconnected from the tool module, and provided with a scanning/pitching shaft for scanning or pitching the tool module, a submersible fan module being selectively connected to or disconnected from the scanning/pitching module, and a first buoyant module for keeping an orientation of the tool module; the base unit includes: a manipulator module internally provided with an actuator driving mechanism, a adsorbing module being detachably mounted on the manipulator module and of adsorbing to a wall, and a second buoyant module for keeping an orientation of the manipulator module; each of at least the scanning/pitching module and the manipulator module is provided with a submersible connecting device being operated in water for engagement and disengagement; configuration and functions of the modular submersible repairing system can be changed or modified according to various purposes of work in the reactor by properly combining those modules; and the modules can be connected together in the reactor by remotely operating the submersible connecting devices.